Quirked Engine
by Erin Tesden
Summary: Iida Tenyo had a lot of expectations to fulfill as a daughter of the Iida family and sister of the Turbo Hero Ingenium. But she never would have imagined that the irritating green-haired boy in her UA practical exam would end up becoming her best friend, her rival and maybe even something more... [Fem!Iida x Izuku]


**As a fan** **of the the series, as well as shiping** **its** **characters,** **I've been wanting to** **write a Boku no Hero** **fic for a while****.** **But I couldn**'**t decide for which pairing** **to write. So as someone who have always** liked** fics applying the Rule 63 (gender bender)** **to some characters, a part of me just thought** , **"What** **if** I **just use Iida?** **The poor guy is almost never shiped with anyone."** **And the picture in my mind of fem!Iida and Izuku together became too hilarious and bizarre but cute to let it go.** **If you are asking, yes, I'm using the pseudo-official gender bender design of Iida drawn by the author himself.**

**Additionally, I have to point out that in order to have the first name of fem!Iida make sense, it was modified by changing the original masculine ending character -ya to the respective feminine ending character -yo.** **The result:** **Iida Tenyo.**

**Finally,** **Boku no Hero and its characters don**'**t belong to me but its respective author.**

* * *

**Chapter 1:** **The glass cannon boy** **and the scary-looking** **class ****president.**

* * *

**Izuku**

* * *

The first fourteen years of life of the shy and adorable cinnamon roll, completely obsessed with heroes and their Quirks, known as Midoriya Izuku had been like some kind of huge sick joke, consisting on a series of unfortunate events followed of one after another without an apparent final. Izuku's tragedy had started when he was only about five years old, his dreams of being a great hero like All Might being trampled after being diagnosed as Quirkless. To make it worse, he not only couldn't count on his always absent father support in such a situation, but he also had to watch how even his poor dear mother didn't thought he could be a hero, just blaming herself for everything.

Perhaps his best friend Bakugou Katsuki would help him to accept the fact that he would never be like All Might? INCORRECT. Before Izuku was even aware of it, Katsuki no longer saw him as Midoriya Izuku, his neighbor and childhood friend, but as Deku, the Quirkless boy from his school that wasn't even worth the air he breathed and which Katsuki could use as a practice dummy to strengthen his explosive Quirk without fearing for any kind of problems. After all, he had a completely amazing Quirk and was going to be the No. 1 Hero in the future, while Deku... He was just a _Deku_, and as such at the most he could aspire in a future it was to maybe, and just maybe, have the opportunity to serve him as bait or third rate cannon fodder...

So nine years went by. However, despite the passage of time Izuku was still fundamentally the same; without a Quirk, without friends, without self-esteem, and without the physical or mental strength to try to change his situation. He only counted with a very well-tuned mind and a lot of Quirks analysis notebooks that not even he himself knew how to use. A deep down part of him had already given up a long time ago on being a hero, and was just waiting for the perfect moment to definitively abandon that childhood dream that he knew wasn't going to happen.

The moment came after All Might rescued him from the sludge villain. It was almost ironic, that the man who represented his dreams, his ideals, would be the one who would destroy them. Izuku had even been stupid enough to hope, even if just for a tiny moment, that All Might would answer yes; that he could be a hero despite not having a Quirk...

But things weren't like that. All Might answer was no, of course. It was at that moment that he stopped being Midoriya Izuku and really became _Deku;_ A boy without hopes or dreams.

And even then... It was impossible for him to ignore and flee from the scene of his ex-best friend, current torturer, suffering at the hands of the same sludge villain that just a few minutes ago had tried to kill him. The same villain who for his fault had escaped from the bottle where All Might had trapped it, the same villain that none of the heroes at the scene knew how to defeat without hurting Katsuki, the very same villain that All Might couldn't catch for a second time now that he had exhausted his Quirk time limit...

Everything was his fault. So despite being a weakling, despite not having a Quirk and feel completely terrified, Izuku found himself running towards Katsuki and the villain. Izuku wasn't strong enough to save Katsuki, but his brave action bought Katsuki enough time to be rescued by a renewed All Might.

As expected, after that the heroes on the scene focused on scolding him for his imprudence and praise Katsuki and his Quirk -although he hadn't done anything besides being a hostage. Despite how unfair that was, Izuku didn't really feel upset about it. Something inside him had been reborn and felt stronger than ever; maybe he never would be a hero like All Might, but he wouldn't surrender or became the _Deku_ that Katsuki thought he was.

It was then that it happened.

_"You__can be a hero!"_

Despite his weaknesses, All Might recognized in Izuku the potential to be a great hero. And not just any great hero, but his successor. All Might was willing to grant him his Quirk, One for All.

So after that, Izuku faced months of hellish training to strengthen his own body enough to access One for All immense power and, hopefully, not explode into a thousand pieces in the process.

Then it came the day to receive the legendary Quirk and put his training to the test: The UA Hero Academy Entrance Examination day had arrived.

Izuku wasn't going to fail.

* * *

Okay, that had been close. Falling to the ground in his face and breaking his nose before even entering the building where the written test would take place didn't seem like a good way to start this. God bless the pretty girl with the gravitational Quirk for help him!

Although from a more optimistic point of view, Izuku had avoided making a fool of himself in the sight of everyone in the UA campus and had a pleasant conversation –NOT- with the girl. His day seemed to go from good to better.

His good humor was still around during the written test, which proved to be easier than he could have imagined. But now it was time to get serious and face the real UA challenge: The practical test.

He couldn't resist the HYPE! The robot villains in the brochures looked so badass! And Present Mic was the one explaining what they have to do! Izuku wondered if he would have the opportunity to ask him for an autograph...

He felt in the clouds. So happy that not even Katsuki presence on the next seat could ruin his good humor, so excited that he couldn't help but start one of his patented unintelligible mumbles, so completely lost in his own world that he didn't even notice the glare of the bespectacled girl sitting a few seats in front of him until it was too late.

"...and you!" The girl's full of disdain voice resounded in the room, with her index finger pointing in Izuku's direction. He turned around, because obviously the girl's hate had to be directed at someone else behind him. "Yes, YOU, the one who keeps mumbling!" Oh, no... It really was him. "IF YOU ARE NOT GOING TO TAKE THIS SERIOUSLY AND PAY ATTENTION TO PRESENT MIC'S INSTRUCTIONS , BETTER GET OUT! SOME OF US TRULY TAKE THIS SERIOUSLY!"

The girl's harsh words pierced him like daggers and he shrank in his seat, feeling completely embarrassed and wanting to disappear from there, trying to ignore Katsuki and the other exam applicants' laughter.

His good luck seemed to be running out. This became even more evident when he noticed that the angry girl from before had been assigned to the same testing place than him.

Now that they were no longer in a dark room, Izuku couldn't help but stare at the girl: She was tall. Absolutely huge. Leaving Mt. Lady aside, for more than obvious reasons, she was easily the tallest girl that Izuku had seen so far in his life, hovering over him with a height about 5'10½.

Her height was complemented by a muscular and curiously angular physical complexion. The face framed by her glasses was as severe as Izuku could have imagined, although her general looks contrasted sharply with the cutesy way in which her jet black hair was gathered in two braids. Ultimately, if Izuku didn't knew the girl was another UA applicant, he could have easily mistake her for an adult woman by her mature appearance.

But for his embarrassment and dismay, the thing about the girl that drew most of Izuku's attention turned out to be her legs... Well. Not in a perverted sense and not exactly her legs, but what appeared to be exhaust pipes coming out from behind the girl's calves, along with the thick engine shape they had.

Izuku's mind ran at a thousand miles per hour trying to decipher the exact nature of the girl's Quirk. The fact that it presented itself physically categorized it automatically as a mutant-type Quirk, and its form and position seemed to indicate they very likely allowed the girl to increase her speed of movement, reminding Izuku by its similarities to the Turbo Hero Ingenium's Quirk.

It was awesome. Izuku had seen a great variety of mutant-type Quirks before, but the vast majority expressed themselves in the form of animal-like physical features. The idea of a mutant-type Quirk in the form of biotic engines acting like natural body parts was completely amazing to him.

Like real engines they must need some kind of fuel, right? Perhaps they worked taking nutrients directly from the user bloodstream? Or as absurd as it could sound, maybe they literally require some kind of real car fuel supplied somehow...? What could their maximum acceleration speed be? What could their drawback be when used excessively...?

And it was then that Izuku became fully aware of the fact he was blatantly eyeing the girl's calves as a total pervert, while she was staring him back with a frown.

Yes, his streak of luck was definitely running out.

* * *

**Tenyo**

* * *

Iida Tenyo had never felt more nervous in her life. And as anyone who knew her enough would know, Tenyo wasn't the kind of girl who collapsed under pressure, but the kind who became almost obsessively focused, and even more serious and perfectionist than usual.

So she didn't think too much about it when she brought Present Mic's attention about the Zero Points not being mentioned in the practical test information and about the green haired boy mumbling incomprehensibly and being a total nuisance in the back row. God, she had never met someone who could be so noisy just by mumbling.

Tenyo sighed and closed her eyes, trying to suppress her irritation. It was just like her older brother and role model, Tensei, always told her. It was admirable to be as serious and responsible as she was, however, there should always be a balance. Knowing how to be less rigid and a little more flexible when the moment merits it. She knew and understood it, but it had always been difficult for her to put such a philosophy into practice, so she remained as the same old rigid and serious Tenyo as always. Intelligent, responsible, hard-working, loved by her family, and respected by her classmates and teachers... And yet, she could count the friends she had had in her whole life with just one hand.

Maybe she would have more luck extending her circle of friends at UA. Thousands of scenes began to float in her mind about her future school life and the difficult road in front of her to inherit the heroic name of Ingenium.

And then she felt as if she was being watched by someone.

She was, by the boy from before, who wasn't even a little subtle about it. She simply glared back to make him stop; the last boy who had looked at her calves with such interest, had decided to prank her by dropping fireworks into her exhaust pipes. It wasn't something nice, at all.

That someone wanting to enter UA could try to do something so awful was an absolute and complete disgrace, but at this point everyone in the test room were rivals, competition, so it was better to be careful of not being sabotaged by someone else. So she kept her attention on the weird trembling boy.

Fortunately, he seemed to have abandoned the idea of doing whatever he was planning to do when he had decided to look at her furtively. Unfortunately, now he seemed to have diverted his attention to a happy-looking girl with brown hair and a bob cut. At the very moment that the boy seemed to have gathered enough courage to approach this girl, Tenyo decided to intervene.

"Could you stop..." She said, not as a request but as an order, as she held the boy 's shoulder with enough force to get his attention.

"E-Eh?" He turned and looked at her with a puppy-like expression. Tenyo had to admit, if he intended to sabotage the competition, he was managing wonderfully at pretending to be completely harmless.

"What, can't you see that girl is already nervous enough without having you bothering her?"

"W-What... I... I just... w-wanted to... Uh..." His voice was so low that Tenyo wouldn't have heard him if he had been just a few inches away from her. Once the boy seemed to have given up on trying to excuse himself for his actions, Tenyo released him and crossed her arms, directing at him one of her _'I__don_'_t understand what__you were trying to do but now I__'__m watching you__'_ patented looks.

"You should leave the others alone and go prepare yourself, or are you truly here just to hinder everyone else?"

"O-Of course n-not!" Curiously, even after raising his voice the boy still gave her the same impression of a puppy throwing small barks. She would have considered it fun if she didn't consider it absolutely annoying. "I-I just wanted to..." Whatever he wanted to say, he ended up being interrupted by Present Mic's voice.

It was time for the practical exam to start.

* * *

2\. 5. 8. 10. 11. 14. 17. 20. 23. 25 points.

It had hardly been more than fifteen minutes since the practical exam had started and she had already accumulated 25 points. Tenyo was completely sure that her grade on the written test would be at least 95, or even a perfect grade. So surely she only needed about 20-25 points more to pass and enter UA.

And even though she should be happy and excited for it, Tenyo was rather distracted and throwing constant looks at the green haired boy's direction.

And no. It wasn't that his performance in battle turned out to be surprising despite his appearance... On the contrary, he seemed like a headless chicken running randomly all over the place. Whenever he found a robot villain to destroy, something seemed to stop him and make him hesitate for only a few seconds, but enough time for any of the others applicants to go and destroy the robots before him.

So if Tenyo had to take a guess, the boy probably hadn't even accumulated a single point yet.

Apparently the boy's frail and weak appearance wasn't a trick to fool the other competitors. He really seemed to lack the initiative and guts to face the practical test properly. She would had almost preferred that the boy turned out to be a cheater after all; the fact that someone who gave so little of himself had even dare to participate at the UA Hero Academy Entrance Examination in the first place, made her feel pretty offended.

27\. 30. 33. 35. 38. 41. 44. 47. 50. 52. 55. 58 points.

She kicked the Three Points with all her strength, trying to get even for all the irritation she felt. Her breathing was heavy and her legs began to feel sore. In her frustration she over-used her Quirk once again...

'Relax, Tenyo. Just breathe and relax...' She repeated in her mind as if it were a mantra, although it sounded more like her brother's voice than herself's. Eventually her mind began to clear up.

Maybe she was being unfair. She watched the green haired boy running towards a Two Points a few meters away from there. Now that Tenyo took the time to observe him better she could see that there was a lot of despair in his eyes, but not of any kind, it was the kind you feel when you fear disappointing those who believed in you. Such feeling was one that she knew very well. After all, she had an absolutely amazing family and it was her duty to fulfill the expectations they had for her, as a daughter of the Iida family and as the sister of the Turbo Hero Ingenium.

"A Quirk not fit for combat, maybe?" She murmured, running in search of more villains to defeat. There was not much time left for the end of the exam, so the amount of remaining robots seemed quite scarce already.

Something she had to admit that called her attention and bothered her a lot about the practical exam was how much it seemed to focus on combat.

Yes. When an average person heard the word hero in whom they thought first was in All Might -Tensei, in her specific case- and the incredible strength of his Quirk, but the fact was that there were a lot of useful Quirks for heroics out there that didn't possess combat capabilities of any kind, like Recovery Girl's Quirk, for example.

Perhaps this boy entered on that category, possessing an amazing Quirk that he unfortunately couldn't use to deal with this type of challenge. From that point of view, it seemed really unfair that the practical exam worked in such an advantageous way for those people with Quirks useful for combat.

Unless... It wasn't so simple.

It was possible that there existed some kind of criterion or special parameter to measure the applicants performance and potential in the practical exam beyond the destructive capabilities of their Quirks... But such a thing didn't appear in the rules ... But perhaps the fact it was a secret was just the point in the first place... But make it a secret could have negative effects by discouraging those with non-combat oriented Quirks to trying enter to UA in the first place too... But perhaps that way they could also qualify the willpower of the applicants... And Tenyo was probably over-thinking the whole thing again.

It was at that moment that Tenyo felt the ground shake and heard the cries of several people located at the test area's center. It didn't take long to understand the reason of the scandal. A robot villain with an intimidating appearance and gigantic proportions: The Zero Points.

Tenyo turned around with the intention of fleeing like the others around her, but stopped in her tracks when she heard a whimper of pain mixed in the crowd noise. Turning back again she catch the source immediately; it was the girl from before, the one the green-haired boy had tried to get close shortly before the practical test started; the poor girl had one leg trapped in the rubble that the Zero Points had caused and couldn't escape. Worse yet, the robot was slowly advancing towards her.

The impulse to run and get the girl out of there arose in her mind, but she dismissed the idea immediately.

This was a test. A test to defeat villains that turned out to be robots, and the colossus a few meters away from her was the only one of all these robots that wasn't worth a single point, the only one that Present Mic had given explicit instructions to avoid and get away if they saw it.

There was no reason to waste time with the Zero Points. There were still a few more robots that she could destroy to fully secure a place in UA, and in addition to that:

1 - There was no way for the girl with the bob cut to be in real danger. This was UA, after all. The entire test worked in a controlled environment and even if someone were to get hurt, the school had Recovery Girl to handle everything in the worst case scenario.

2 - Maybe everything was just a trick, with the cute girl pretending to be in danger. An UA's trick to make some impulsive idiot to try to attack the Zero Points. After that, the poor idiot would end up losing several points or even being disqualified from the whole practical test for going against Present Mic's order of avoid the Zero Points.

Everything made sense in Tenyo's mind. It was logical. Considering the fact that all the other applicants were also fleeing, it seemed to be true... But even so, a part of her wanted to run to rescue the girl anyway, no matter how stupid it was or the consequences it was going to have. That not-logical-at-all part of her was screaming that it was the right thing to do.

'What would Tensei do?' She repeated stupidly in her mind, although she already knew the answer.

Tensei would have rescued the girl. He would ran to save her from the very start. So, why was she just standing there watching? What kind of hero was she supposed to be if she really was leaving someone in danger for such cold reasons? ...She had to do something.

Having finally decided, Tenyo bowed slightly, ready to activate her Quirk.

It was then that a greenish blur passed by her side. It was that boy again, running in the opposite direction to all the other applicants fleeing from the area.

For a moment it crossed her mind to yell if he was blind or genuinely hadn't noticed that he was running towards the almighty robot that was easily destroying and trampling everything that was nearby it. But the words never came out of her mouth

The expression on the boy's face had left her stupefied: Where previously she could only see fear and insecurity, now Tenyo could distinguish a very strong determination.

Oh no. He also wanted to save the girl from the Zero Points. The same guy who apparently hadn't been able to make a single scratch on any of the other robot villains, now wanted to go against the Zero Points.

"IDIOT!" She actived her Quirk and forced it to go beyond its maximum capabilities. She had to keep the imprudent boy from being crushed by the Zero Points and also get the girl out of the rubble or she was never going to forgive herself...

Once she was close enough, Tenyo moved her arm forward ready to take the boy from his shirt and throw him as far away from the Zero Points as possible.

However, things didn't turn out according to the plan. Before her fingers could get a hold on to the boy's shirt, Tenyo watched as he simply disappeared from her vision in a single instant, as if it were a magic trick or as if he had teleported himself away. His disappearance was followed by a thunderous sound of concrete breaking, and before Tenyo could even react, she felt like an immense amount of wind impacted against her whole body, as if she had been in the middle of a huge explosion, pushing her several meters backwards and causing her to fall to the ground on her back.

Tenyo eyes, fixed on the fake blue sky, immediately grasped a figure flying over the test area towards the Zero Points. The green hair immediately revealing who it was.

The boy hadn't disappeared at all. He had simply jumped before she had the opportunity to stop him.

Leaning a little to sit, she watched dumbfounded as the boy's whole body tensed and he moved his arm back, before shouting 'SMASH!' and launching a punch towards the Zero Points. That alone was enough to generate a powerful wind blast that displaced all the debris that trapped the girl's leg, and pierced through the huge and armored body of the robot villain as if it were made of cardboard, completely obliterating it.

Everything from that moment happened pretty fast. The cute girl, with a leg hurt but relieved to be able to move freely once again, managed to float and prevent the green haired boy to fall to the ground and end up like an omelet. Just a few seconds later it sounded the alarm warning that the practical test was over and Recovery Girl appeared walking towards the boy.

Even from a distance it was obvious how hurt he was; the arm he used to attack the Zero Points was completely broken, as well as his two legs, probably as a result of the great jump he had made.

She remained there, following the boy with her eyes as he was taken out of the test area on a stretcher.

Now finally everything made sense. The fact that the boy was so nervous and fearful throughout the test and how he didn't seemed able to muster enough courage to attack any of the robot villains.

Despite possessing such immense power, his ability to handle such strength seemed very low. It was even possible that he had acquired his Quirk recently, which would explain perfectly his poor control. He probably was aware that he only had one or two attacks using his Quirk before ending completely incapacitated to continue the test...

So when he ran from one place to another, looking like he didn't knew what to do, he probably was just waiting for the perfect moment to use those few attacks he had available. Wanting to get enough points in the practical exam without wounding himself too much or hurting the other applicants around him in the process.

Maybe he planned something like cornering several villains in one place and defeat them all with just one attack. The possibilities with such a powerful Quirk were many... But in the end, what the boy did was sacrifice his opportunity to pass the practical exam in order to save someone in trouble...

After being briefly examined by Recovery Girl, who helped her heal a few scratches she had made when she fell to the ground, Tenyo was dispatched from the building with the other applicants and went to the campus parking lot, where Tensei was waiting in his car.

After an exchange of greetings, she got on one of the back seats and put on the seatbelt. Tensei turned on the car engine and started driving.

She remained thoughtful for a good stretch of the travel until Tensei broke the silence.

"Something wrong, little sister?" He said kindly. "You look kind of dizzy." He gave her a worried look in the rearview mirror. "You shouldn't worry so much, we both know there's no way you've done it wrong."

"Ah." She blinked, taking a moment to properly understand her brother's words. "... It's not that, Tensei-oniisama, I'm completely sure that I passed both the written and the practical exam..." She commented as if it didn't matter.

"I can see that someone is getting a little smug, he, he." Tensei joked.

"... But I still lost." She added after a while, in a whisper.

That was the easiest way to put it. She had lost.

As unfair as it was, she seriously doubted that the green haired boy -how much she wanted to know his name now- was going to be accepted by UA, even if his written test score turned out to be perfect. But at the end of the day, even if she didn't meet him ever again, nothing would change the fact that in regards the long and difficult road to become a hero, she had been completely surpassed by him.

The memory of him flying through the air and destroying Zero Points was still recorded in her mind, causing a strange pressure and feeling of warmth in her chest.

"... I wonder if I'm being naïve, hoping that he will end up being accepted by UA anyway." She said softly.

"Did you say something, little sister?" Tensei questioned once more. His sister wasn't the most social person in the world, but she wasn't that reserved either, especially when he was around her. Under normal conditions, Tensei would have expected her to talk non-stop about her experience at UA, things like complaining about having found spelling errors in the written exam questions, or commenting on how some applicants acted very inappropriately or disrespectfully during the tests, etc. That was the way how his beloved and rigid younger sister was. To be so quiet, there had to be something upsetting her.

"There was a boy in my practical exam, he was incredibly noisy in his own weird way and managed to make me lost my cool several times..." Tensei smiled at her sister comment; that was his typical little sister. "But he also proved to have the courage and potential to be a great hero like Tensei-oniisama... In that sense, I feel like he defeated me completely." Tenyo's voice sounded slightly discouraged. Tensei looked at her fondly; he had always felt immensely proud of being considered her role model; of being hold in such a high esteem by her. Especially when, from Tensei's point of view, it was Tenyo who was the better of them both; that she was the one truly worthy of such admiration. All that modesty was a really nice and adorable trait of her little sister. But the fact that now she seemed to be slightly jealous of this boy wasn't only adorable but kind of funny too.

"Again, don't worry too much little sister. You still have a long road ahead... And if you really think this guy left you behind, all you have to do is not to give up. Keep up going, learn from him and your mistakes and improve. Building a healthy rivalry will help you tremendously to grow both as a person and as a hero." And if his little sister needed something, that was more people close to her in whom she could trust to the same degree that she trusted him.

After completely digesting his words, Tenyo put on a sulky expression -which Tensei found simply adorable- and sighed.

"That's the problem..." Tensei raised an eyebrow, telling her to continue. "I seriously doubt that UA is going to send this boy a letter of acceptance." Ah. Tensei nodded; so this guy probably hadn't accumulated enough points in one of the tests to pass. A pity; if his little sister saw him with such good eyes he surely had to be an exemplary youngster."...A-Although it would be nice if he was accepted." Tenyo said finally, and Tensei hit the brakes suddenly. "E-E h. Is something wrong, Tensei-oniisama?" She asked, surprised that her brother had stopped the car so suddenly, there wasn't a red light nearby or anything.

"Ah, it's nothing, little sister... Just remember to be more positive! I'm sure you're worrying for nothing and this young man you are talking about actually make it better on the tests than you think. I'm sure UA is going to accept him. Hopefully they may even assign him to your same class!" He commented trying to sound natural, as if he hadn't seen his beloved little sister blushing and putting a dreamy expression while talking about this mysterious young man -maybe future brother-in-law- just a moment ago.

"T-That would be great!" Tenyo answered, already in a better mood, while nodding repeatedly.

Tensei just smiled and kept driving.

* * *

**Well, this chapter ends here. I hope you liked it.**

**English is my second language so I probably committed a lot of mistakes in the redaction. If you saw something too awfull please put it at the reviews to correct it. (I really need a beta reader…)**

**In the next chapter, the reunion of our pair of idiots and the practice battle (I think im going to skip the whole apprehension of Quirks thing because I honestly can**'**t find how to create interesting interactions between the characters in it).**

**Make your comments and constructive criticism in the reviews, and follow if you like. Until next time (in a month or something).**


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